1. Field of the Invention
The present invention is concerned with connectors for joining together the end portions of capillary tubes for use in a gas chromatograph, for example, and is more particularly concerned with providing a connector between capillary tubes which is easily assembled and has a number of leak-proof seals and provides for uninterrupted flow of the fluids such as a carrier gas that flow through the tubes.
2. Description of the Prior Art
Chromatographers and scientists of various disciplines have a need to connect fused silica or stainless steel tubes in end-to-end fashion with a connector that does not detract from chromatographic properties and does not interfere with the flow of fluids such as a carrier gas through the tubes. The connecting together of the end portions of thin wall fused silica or stainless steel tubes with outside diameters ranging from 0.1 to 1.0 mm and inside diameters ranging from 0.01 to 0.8 mm is difficult because the connection may introduce unswept regions or gaps that cause eddies and flow turbulence. Also, the connector may absorb active compounds which decrease the accuracy of the quantitative and qualitative analysis.
U.S Pat. No. 4,529,230 which issued on Jul. 16, 1985 addressed a number of these problems, and disclosed a connector 10 which used a double tapered Vespel ferrule 13 that aligned and sealed the ends of the capillary tubes 11. However, this connector 10 was difficult to use because it was awkward to assemble. Also, it caused adsorption of basic and other compounds with active functional groups. In addition, prolonged use of this connector at temperatures above 325.degree. C. caused the Vespel ferrule to shrink and leak.
Two publications appeared in 1986, Simple Press-Fit Connectors for Flexible Fused Silica Tubing in Gas-Liquid Chromatography, Journal of HRC & CC, Volume 9, May 1986, pp. 295-297, and A Simple, Universal Joining System for Glass to Silica Capillary Tubing, Journal of HRC & CC, Volume 9, August 1986, pp. 481-482, which appeared to address most of the problems which occur when trying to connect the tips of two fused silica tubes. The press-fit connectors disclosed by these articles formed a good seal and no loss of inertness or adsorption of active analytes occurred. However, this technique was not dependable or reproducible. Sometimes the tubes disconnected unpredictably or leaked. Sometimes the connector did not seal because the glass taper was not made properly. However, a big problem was that these connectors would not function above about 325.degree. C. because the polyimide coating on the flexible fused silica tubing would dry out and loose its sealing ability.